The present invention relates to an optical lens system with a variable focal length, and more particularly to a focusing method in an optical lens system with a variable focal length including a wide-angle setting.
Recent years have been wide-spread use of so-called zoom lenses. Standard zoom lenses, in particular, including wide-angle to telephoto regions or settings with a standard angle of view therebetween are becoming one of the most popular lenses because of a handy size thereof. As is well known, automatic focusing (hereinafter referred to as an "AF") lenses which have started to be used in compact cameras are employed in many cameras since they are quite convenient to use.
However, few arrangements are known in which a zoom lens and an AF mechanism are combined so that they cooperate with each other. One reason is that since the zoom lens is necessarily large in size, its incorporation in a compact camera would make the camera no longer compact. There are a very few examples in which an AF mechanism is combined with a zoom lens designed for a single-lens reflex camera. However, such an assembly requires a motor for driving the AF mechanism, a power supply, and an equipment for measuring the object distance, and hence is larger, heavier, and costlier than an ordinary combination of a single-lens reflex camera and a zoom lens. All of the known examples employ a front-group moving system called front lens focusing for focusing the lenses. The front lens group is generally large in diameter and heavy and requires to be driven by a large-power motor. The front-group moving system is therefore disadvantageous in that it requires a large expenditure of electric power, a large-size power supply such as a battery, and results in an overall large size.